The programme for Skin Deep makes it very clear that this is "an operetta" - presumably in case anyone should be inclined to approach David Sawer's new theatre piece for Opera North too seriously, or expect his elegant, economical score to assume any real dramatic or emotional responsibility. In fact, a bit more seriousness, or at least a firmer grounding in reality, might have made this comic take on the cosmetic surgery industry a lot funnier, and honed its satirical edge.

The librettist is Armando Iannucci, drafted into the project because Sawer envisaged a work that would draw on the world of television satire, and Iannucci's programmes - The Day Today, The Thick of It - seemed a good starting point. But the text never quite hits the right tone. There's too much of it, for a start. Words flash by, so that the jokes embedded in them go for nothing. Characters are paper-thin, and the farther the plot moves from reality, the less involving and funny it becomes.

The first two acts are set in the clinic of cosmetic surgeon Dr Needlemeier, whose motto is: "Putting right what nature got wrong." While the rich and famous have their anatomies tweaked, Needlemeier is working on an elixir of youth, using body parts as ingredients. By the third act, he has set up a gated community with those who have undergone his treatment. When volunteers are needed to make more elixir, things turn nasty. Needlemier and his mistress end up gruesomely transformed while everybody else accepts that it is imperfections that make them human.

It's hard to see what Sawer's music could have done to rescue this contrived, feeble plot, with humour not far removed from a Carry On film. However, under conductor Richard Farnes, Opera North do it proud musically. The cast includes Geoffrey Dolton as Needlemeier, Janis Kelly as his wife and Heather Shipp as his mistress Donna, with Mark Stone as an actor who mislays one of his testicles in the elixir-manufacturing process.

Richard Jones's coy staging, with designs by Stewart Laing, isn't one of his more distinguished efforts. It hits its lowest point in the final scene when the chorus appear in wrinkled, flesh-coloured body-stockings - complete with false breasts, penises and pubic hair - to illustrate the Candide-like moral that we should all accept each other as we are. It's a limp ending to a disappointingly limp piece.